The present invention relates to a tracheostomy tube particularly a tracheostomy tube having fenestrations in the outer cannula and having a disposable inner cannula.
Tracheostomy tubes have been used for some time to provide a bypass supply of air or mixture of gases to a patient having an obstruction in the larynx or the pharynx area of the throat. The distal end of the tracheostomy tube is inserted into the trachea through an incision in the patient's neck below the obstructed area. The proximal end of the tube remains outside the trachea in communication with ambient air to permit passage of such air into the trachea. The proximal end of the tube can also be attached to a respiratory device to assist the patient's breathing. The distal end also includes an inflatable cuff to seal the distal end of the tube within the throat to further assist the patient's breathing on the respiratory device, as described in U.S. Pat. No. 3,659,612 assigned to the assignee of the present invention. U.S. Pat. No. 3,693,624, also assigned to the assignee of the present invention, discloses a tracheostomy tube having an inner cannula which serves as an inner liner of the outer cannula and can be removed, cleaned and then replaced.
A fenestrated tracheostomy tube is utilized for special applications when a patient is being weaned from the use of the tracheostomy tube. The tube includes fenestrations through the upper surface of the outer cannula in communication with the normal airway of the patient's throat. Periodically, the sealing cuff is deflated, the inner cannula is removed and the outer cannula is plugged, resulting in the patient breathing through the fenestrations and upper airway in a normal manner. This can initially only be done for a short period of time. Then the plug is quickly removed and replaced with the inner cannula, if necessary, to open the tracheostomy airway, then the cuff can be reinflated if periodic ventilation is required. This process is gradually repeated and extended in duration until the patient is able to use the normal upper airway, at which time the tracheostomy tube can be removed.
Current tracheostomy tubes have been developed in which the inner cannula is disposable, as disclosed in U.S. Pat. No. 4,315,505 assigned to the assignee of the present invention. This patent is incorporated herein by reference and particularly discloses an inner cannula constructed from a soft, flexible polymer material such as polyvinyl chloride (PVC) and which can be inexpensibly manufactured using plastic injection molding techniques or can be made from a two-part process including an extrusion step followed by a di-electric end forming step. The disposable inner cannulae are made of thin flexible material which become easily distorted following their manufacture due to their handling, molding characteristics and relaxation of internal stresses; which causes the inner cannula to tend to become oval at the distal tip and tends to increase the radius of curvature. Upon insertion of the somewhat distorted disposable inner cannula into a fenestrated outer cannula, the distal tip of the inner cannula encounters interference or engagement with the fenestration. This problem is particularly apparent where the fenestration is in the form of a generally elliptically or oval shaped opening along the center line of the outer surface (see FIG. 1) as is common in known prior art. The flexible inner cannula which has a generally vertically oriented oval distal tip and has an increased radius of curvature, now upon insertion tends to be forced to slide along the inner surface of the upper wall. The upper portion of the flexible distal tip, therefore generally expands into the oval fenestration resulting in interference when the upper distal tip encounters the vertical rear wall of the fenestration which prevents or delays insertion of the inner cannula into the tube.
The function of the fenestration requires that the opening be generally along the upper surface of the tracheostomy tube. The prior art has incorporated a large oval opening, as previously described which tends to be inadequate due to the interference. The prior art has also incorporated a series of small multiple holes along the outer surface which do not interfere with the inner cannula but tend to become easily clogged and are therefore also considered to be inadequate. The prior art has also utilized a plurality of longitudinal slots spaced away from the center line to reduce such interference; although this is an improvement, the upward air flow is reduced and interference also sometimes occurs and therefore this configuration is also considered to be inadequate.